LoRa Flood Sensor Development Series - Part 3 PCB Placement Guide

LoRa Flood Sensor Development Series – PCB Placement Guide

Design Overview

We are using an existing enclosure for a shell-fit PCBA design.

• Enclosure outer diameter: 50mm
• Due to waterproof design, the internal space is quite limited.
• The other side must accommodate a coin cell battery, therefore only single-sided component placement is allowed.

---

Step 1: Determine PCBA Outline

1. Locate the internal PCBA dimension drawing of the enclosure.
2. Open the drawing with CAD software (AutoCAD, DraftSight, etc.).
3. Carefully study the drawing and identify keep-out areas (regions where components are prohibited).

---

Step 2: Create Board Outline in KiCad

1. Open your project in KiCad.
2. Import the PCBA outline:
   • Go to File → Import → Graphics (or use DXF import).
   • Select the prepared dimension file and import it.
3. After import, delete all unnecessary graphics and layers.
4. Keep only the final PCBA board outline on the Edge.Cuts layer.

---

Step 3: Component Layout Guidelines

The layout is relatively simple due to single-sided constraints. Follow these rules:

• Single-sided component placement only.
• Place filtering capacitors as close as possible to the power pins of ICs.
• Arrange components following the signal flow direction.
• Position connectors, electrodes, and buttons exactly according to the mechanical drawing specifications.
• Pay special attention to height restrictions — check component height in limited clearance areas.
• Reserve enough space for the coin cell battery on the opposite side.

---

3D Effect Verification

After completing the layout and assigning 3D models in KiCad:

• Use View → 3D Viewer to check the overall assembly.
• Verify clearance with the enclosure and coin cell battery.
• Ensure no component interference with the waterproof shell.

---

Key Design Principles Summary

• Strictly follow mechanical constraints and keep-out zones
• Prioritize signal integrity and power integrity
• Place decoupling capacitors near power pins
• Maintain sufficient clearance for battery and waterproofing
• Pay attention to component height restrictions
• Optimize component placement according to signal flow

---